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January 12, 2009

Drafting Settings Part 3 -- Object Snaps

Part 3 in our tour of the Drafting Settings dialog box is all about Object Snaps, or "osnaps" for short.

Just like the other two tabs we've seen already, the Object Snap tab has on/off toggles at the top for both the snaps themselves and tracking.

Object Snaps enable you to precisely grab a point on an object, such as an endpoint of a line or the center of a circle, to make sure that geometry that you create or modify ends up exactly where you want it to be. Nothing's more frustrating than receiving a drawing, opening it up, and realizing it that whoever created it didn't use any object snaps. It can mean that "intersecting" lines don't actually touch, or that lines that are supposed to be precisely 6" apart are some fractional amount off from that. That can create some real headaches. (If you've ever seen a drawing like this, you'll know what I'm talking about. If not, be grateful.)

Osnaps can be activated as a one-time snap, or set to be on all the time. The checkboxes in this tab are for the "all the time" osnaps, or running osnaps. The screenshot above shows my personal preference for running osnaps. One osnap that I never set as running is Nearest. There are times when it's an appropriate snap to use, but mostly I'm concerned that instead of grabbing an endpoint or midpoint as I want, I'd end up with a "nearest" point instead. I'm not trying to say that Nearest should never be used as a running osnap, just...be careful.

If you only need a particular object snap once in a while, there are two ways you can get it without turning it on permanently. First, you can type its command line shortcut, usually the first three letters of the snap name (END, MID, CEN, etc.). Or you can hold down SHIFT and right-click, and pick your osnap from the shortcut menu that pops up.

The icon next to each osnap name is the shape you will see when that particular snap is active. The example below shows the endpoint and midpoint icons. To cycle between nearby locations for running osnaps, press the TAB key until you see the icon you want.

Now, when you hover over an osnap location long enough for its tooltip to appear (as I did in the above image), something special happens. That point has now been "acquired", and you can track from it to find another point in the drawing aligned with that one. It's called Object Snap Tracking (or otrack for short), and it's very similar to Polar Tracking -- see Part 2 for more on tracking angles.

To see how this works, imagine that you wanted to draw a line that started at the center of a rectangle. Instead of drawing a construction line from corner to corner, snapping to its midpoint, drawing the line, and then erasing the construction line, let's use Object Snap Tracking instead.

First, I'll hover over the middle of one side of the rectangle until the midpoint icon appears. Then I'll move the cursor up until a dotted line appears, telling me that otrack is active.

Next, I have to go get the other side. Notice that there's still a small "+" at the location of the first midpoint, identifying it as a tracking point.

Finally, when I move my mouse close to the intersection of these two dotted lines, they BOTH appear. I can then left-click to begin drawing my line.

That may seem like a complicated explanation, but I promise you it takes 10 times longer to explain it than it does to use it.